1. Field of the Invention
The present invention relates to a fuel supply apparatus for a vehicle, and particularly to an in-tank type fuel supply apparatus having a subtank, containing a fuel pump, disposed at the bottom of a fuel tank.
2. Description of Related Art
In-tank type fuel supply apparatus proposed in a related art includes a subtank-on-bottom type fuel supply apparatus having a construction wherein a subtank with a built-in fuel pump is held vertically movably by a bracket for covering an opening of a fuel tank in which the fuel supply apparatus is installed and the subtank is pressed against the bottom of the fuel tank by a spring.
In U.S. Pat. No. 5,669,359 there is proposed a subtank-on-bottom type fuel supply apparatus having a construction wherein a subtank is joined by a barlike elastic member to a bracket for covering the opening of a fuel tank and the subtank is pressed against the bottom of the fuel tank by a bending urging force of the barlike elastic member.
These subtank-on-bottom type fuel supply apparatuses have the advantage that because a fuel inlet in the bottom face of the subtank always follows the fuel tank bottom, irrespective of the attitude of the vehicle and the shape of the bottom of the fuel tank, the supply of fuel to the fuel pump can be made smooth, furthermore, when a fuel level detecting apparatus is provided in the subtank, the fuel level can be detected accurately irrespective of changes in the position of the bottom of the fuel tank.
However, with the first of the aforementioned subtank-on-bottom type fuel supply apparatuses, because a subtank having a certain necessary capacity must be inserted into the fuel tank through an opening in the fuel tank having a limited size, inevitably the height of the subtank must be increased. As a result, this type of fuel supply apparatus cannot be used in a shallow fuel tank. Because fuel tanks can have any of a variety of shapes depending on the type of the vehicle, then, this type of fuel supply apparatus can only be used in a limited number of fuel tanks. Of course, if the opening of the fuel tank were to be enlarged, it would be possible to reduce the height of the subtank while maintaining the necessary capacity; however, enlarging of the opening is undesirable from the standpoints of maintaining the strength of the fuel tank and preventing the diffusion of fuel vapor.
With the second of the aforementioned subtank-on-bottom type fuel supply apparatuses described above, on the other hand, especially if the subtank has a float or the like for level detection, the front-rear direction dimension of the subtank after it seats on the bottom of the fuel tank is much greater than its height. Consequently, with the subtank-on-bottom type fuel supply apparatus using a barlike elastic member disclosed in the above-mentioned patent, when the subtank is inserted into the fuel tank through the fuel tank opening, it has been necessary to turn the subtank through about 90.degree. inside the fuel tank.
Accordingly, the barlike elastic member has had to be strongly elastically deformed while this turning and insertion operation is carried out, the operation has been complicated, and also special construction measures such as increasing the strength of the relevant portions of the bracket and the subtank supporting the ends of the barlike elastic member have been necessary. Of course, if the opening of the fuel tank were to be enlarged, the insertion of the subtank would be easy; however, as mentioned above, enlarging of the opening is undesirable from the standpoint of maintaining the strength of the fuel tank and preventing the diffusion of fuel vapor.
A bottom-reference fuel sender gauge (fuel level sensor) is also known, for being mounted on a subtank pressed against a fuel tank bottom by a spring. Unlike a fuel sender gauge of the type to be fixed to the top of a fuel tank, because this bottom-reference fuel sender gauge can follow vertical movements of the fuel tank integrally with the subtank, it can measure the position of the liquid surface relatively accurately.
However, in recent years, to make effective use of vehicle space, the trend has been for fuel tanks to become flatter, and this kind of fuel tank which in vertical section is flat will bend under fuel weight or under tank internal pressures accompanying vapor formation from fuel.
As a result of such bending, fuel collects in the bent part, and when the liquid surface height at the position of the float consequently falls with respect to the fuel tank bottom, notwithstanding that the actual amount of fuel in the fuel tank has not changed, the angle of the float with respect to a reference position constituting a fuel empty point decreases. Consequently it is erroneously detected that the amount of fuel remaining has decreased. That is, even with a so-called bottom-reference fuel sender gauge, if the liquid surface position at the float changes relatively due to fuel there will be an increase in erroneous collecting in a bent part, the error of the liquid position detection.
In U.S. Pat. No. 5,669,359 there is disclosed an apparatus is disclosed wherein a subtank and a flange are joined by a spring capable of following up bending and the subtank is made to follow up bending while changing its horizontal position relative to the flange position.
However, because, as a consequence of the structure of the apparatus, repetitive stress acts on the spring constantly, and furthermore the frequency of repetition and the size of this stress depend on the pattern of change of the internal pressure of the fuel tank, there are problems in securing an adequate apparatus lifetime.
Also, to the extent that the horizontal position of the subtank relative to the flange position is liable to shift under outside forces, it may not be possible to secure a subtank reserve when parking on a slope, and a desired turning performance cannot be obtained.